This invention relates to spark ignition direct injection engines and to injectors for such engines having a plurality of spray holes formed in an advantageous pattern.
In recent years many internal combustion engines have been proposed which have tried to improve fuel consumption by direct fuel injection into the cylinder. By injecting during the compression stroke at part load conditions, a suitable amount of fuel vapor is collected around the spark plug, and overall lean operation is realized. Several four valve SIDI engines have been disclosed. Many of these use a swirl type fuel injection device in which the fuel is injected with a swirl component. Also proposed has been a slit (fan) spray configuration.
FIG. 1 schematically represents a prior art engine 10 having a piston 12 with a bowl recess 14 positioned toward the intake valve side of the cylinder not shown. An injector 16 provides a generally cone shaped swirl type spray 18 which is injected toward the bowl recess 14 as the piston rises on the compression stroke. However there is an initial spray 20 which does not have a swirl component. This initial spray has a relatively large spray particle size and, because atomization is poor, it results in smoke generation and unburned hydrocarbons (HC). Further, because even the main spray shape 18 is restricted to a cone shape the fuel is not optimally distributed on the piston. The lower part of the cone shaped spray directly below the injector will contact the piston first and can cause a liquid film on the surface which generates smoke. Also, portions of the spray may interact with the piston outside of the bowl recess creating a dispersed cloud which adversely affects combustion and unburned HC emissions. Additionally, the spray angle 22 can vary (become smaller) due to conditions of fuel temperature, cylinder pressure and the like so that it is difficult to control the mixing condition of the spray.
The present invention provides a spark ignition direct injection (SIDI) engine having a combustion chamber defined in part by a piston bowl recess and a fuel injector for such an engine. The injector includes an injection nozzle for directing a fuel spray into the combustion chamber wherein the nozzle has a plurality of spray holes formed in a generally semicircular pattern. The pattern of the fuel spray at a fixed distance below the injector nozzle under atmospheric conditions approximates a semicircle formed by an arc having ends connected by a straight line and wherein intermediate positions of the sprays are spaced along the arc and the straight line while end sprays are located at the intersection of the arc and straight line.
The spray pattern is formed by a nozzle having multiple spray holes formed in an approximate semicircle joined at its ends by a straight line. The spray holes lying on the semicircle, including those at the ends of the straight line, have axes extending from the center of a part spherical fuel sac within the injector nozzle, while the intermediate spray holes along the straight line have centers extending from above the center of the injector nozzle fuel sac. The intermediate holes are thereby offset slightly below the straight line in order to increase turbulence of the fuel in the intermediate spray holes to be equivalent with the holes located around the periphery of the arc so that penetration of the sprays from all the spray holes is essentially the same and result in the desired semi-circular spray pattern.
The approximately semicircular spray hole pattern and the resulting semicircular fuel spray pattern can provide a fuel spray which is contained almost entirely within the piston bowl recess and is largely vaporized before striking the surface of the piston so that production of smoke is minimized and fuel economy is maximized.
Preferably the spray holes of the nozzle have a length over diameter (L/D) ratio of 2.0 or less. In tests of a specific embodiment, five spray holes arranged with four holes around the periphery of the semicircular arc and a central (intermediate) hole between the end holes on the straight line was found to provide the best in smoke and fuel economy. However, six holes were also projected to fall within the desired smoke limit. It is anticipated that for larger engine sizes, an additional number of holes up to around ten or more may be utilized to obtain similar results.